1. Field of the Invention
The present invention relates to a lens barrel provided in image pickup apparatuses such as a film camera, a digital camera, etc. and to an image pickup apparatus provided with the lens barrel.
2. Description of the Related Art
Conventionally, there is a known lens barrel provided with a zoom drive mechanism that regulates rotations of lens holding frames that hold lenses, respectively, by a rectilinear barrel, engages cam followers formed on the lens holding frames with cam grooves formed on a cam barrel, and moves the lens holding frames by rotating the cam barrel to move the lenses to predetermined positions.
A demand to increase a magnification in recent years tends to increase the full length under an extended condition and to enlarge a lens barrel. On the other hand, there is a demand to minimize a camera thickness under a lens retracted condition.
Although a multiple connection of short lens barrels may be effective to decrease the camera thickness under the lens retracted condition, it is difficult because there are many limitations when cam grooves corresponding to the lens barrels are formed on a cam barrel without crossing.
Japanese Laid-Open Patent Publication (Kokai) No. 2004-085934 (JP 2004-085934A) suggests a lens barrel that has a cam barrel in which cam grooves having the same locus are formed at different positions in an optical axis direction and a circumferential direction and a rectilinear barrel in which cam followers are formed at different positions in the optical axis direction and the circumferential direction so as to engage with the respective cam grooves.
In this suggestion, since movement of a lens group guided by the rectilinear barrel in the optical axis direction can become longer than the length of the cam barrel in the optical axis direction, the length of the cam barrel in the optical axis direction can be shortened, which can decrease the camera thickness under the lens retracted condition.
Japanese Laid-Open Patent Publication (Kokai) No. 2009-9115 (JP 2009-9115A) suggests a technique that forms a cam groove on a projected part of a cam barrel that is projected toward an image surface side in an optical axis direction so as to increase a stroke of the cam groove in the optical axis direction in order to decrease the camera thickness under the lens-retracted condition.
However, in the technique of JP 2004-085934A, since a motion of the lens group guided by the rectilinear barrel in the optical axis direction becomes unstable when the cam follower of the rectilinear barrel is off the cam groove of the cam barrel, a zoom operation of the lens barrel may become unstable, as a result.
In the technique of JP 2009-9115A, since the lens barrel needs the rectilinear barrel that is arranged inside the cam barrel and a cylinder member that regulates rotation of the rectilinear barrel, i.e., needs three or more barrels, the configuration of the lens barrel becomes complicated and the technique cannot be applied to a two-barrel configuration.